The term "electrotransport" as used herein refers generally to the delivery of an agent (eg, a drug) through a membrane, such as skin, mucous membrane, or nails. The delivery is induced or aided by application of an electrical potential. For example, a beneficial therapeutic agent may be introduced into the systemic circulation of a human body by electrotransport delivery through the skin. A widely used electrotransport process, electromigration (also called iontophoresis), involves the electrically induced transport of charged ions. Another type of electrotransport, electroosmosis, involves the flow of a liquid, which liquid contains the agent to be delivered, under the influence of an electric field. Still another type of electrotransport process, electroporation, involves the formation of transiently-existing pores in a biological membrane by the application of an electric field. An agent can be delivered through the pores either passively (ie, without electrical assistance) or actively (ie, under the influence of an electric potential). However, in any given electrotransport process, more than one of these processes may be occurring simultaneously to a certain extent. Accordingly, the term "electrotransport", as used herein, should be given its broadest possible interpretation so that it includes the electrically induced or enhanced transport of at least one agent, which may be charged, uncharged, or a mixture thereof, whatever the specific mechanism or mechanisms by which the agent actually is transported.
Electrotransport devices use at least two electrodes that are in electrical contact with some portion of the skin, nails, mucous membrane, or other surface of the body. One electrode, commonly called the "donor" or "active" electrode, is the electrode from which the agent is delivered into the body. The other electrode, typically termed the "counter" or "return" electrode, serves to close the electrical circuit through the body. For example, if the agent to be delivered is positively charged, ie, a cation, then the anode is the active or donor electrode, while the cathode serves to complete the circuit. Alternatively, if an agent is negatively charged, ie, an anion, the cathode is the donor electrode. Additionally, both the anode and cathode may be considered donor electrodes if both anionic and cationic agent ions, or if uncharged or neutrally charged agents, are to be delivered.
Furthermore, electrotransport delivery systems generally require at least one reservoir or source of the agent to be delivered, which is typically in the form of a liquid solution or suspension. Examples of such donor reservoirs include a pouch or cavity, a porous sponge or pad, and a hydrophilic polymer or a gel matrix. Such donor reservoirs are electrically connected to, and positioned between, the anode or cathode and the body surface, to provide a fixed or renewable source of one or more agents or drugs. Electrotransport devices also have an electrical power source such as one or more batteries. Typically, one pole of the power source is electrically connected to the donor electrode, while the opposite pole is electrically connected to the counter electrode. In addition, some electrotransport devices have an electrical controller that controls the current applied through the electrodes, thereby regulating the rate of agent delivery. Furthermore, passive flux control membranes, adhesives for maintaining device contact with a body surface, insulating members, and impermeable backing members are other optional components of an electrotransport device.
All electrotransport agent delivery devices utilize an electrical circuit to electrically connect the power source (eg, a battery) and the electrodes. In very simple devices, such as those disclosed in Ariura et al U.S. Pat. No. 4,474,570, the "circuit" is merely an electrically conductive wire used to connect the battery to an electrode. Other devices use a variety of electrical components to control the amplitude, polarity, timing, waveform shape, etc of the electric current supplied by the power source. See, for example, McNichols et al U.S. Pat. No. 5,047,007.
To date, commercial transdermal electrotransport drug delivery devices (eg, the Phoresor, sold by Iomed, Inc. of Salt Lake City, Utah; the Dupel Iontophoresis System sold by Empi, Inc. of St. Paul, Minn.; the Webster Sweat Inducer, model 3600, sold by Wescor, Inc. of Logan, Utah) have generally utilized a desk-top electrical power supply unit and a pair of skin contacting electrodes. The donor electrode contains a drug solution while the counter electrode contains a solution of a bio-compatible electrolyte salt. The "satellite" electrodes are connected to the electrical power supply unit by long (eg, 1-2 meters) electrically conductive wires or cables. Examples of desk-top electrical power supply units which use "satellite" electrode assemblies are disclosed in Jacobsen et al U.S. Pat. No. 4,141,359 (see FIGS. 3 and 4); LaPrade U.S. Pat. No. 5,006,108 (see FIG. 9); and Maurer et al U.S. Pat. No. 5,254,081 (see FIGS. 1 and 2). The power supply units in such devices have electrical controls for adjusting the amount of electrical current applied through the electrodes. The "satellite" electrodes are connected to the electrical power supply unit by long (eg, 1-2 meters) electrically conductive wires or cables. Wire connections are subject to disconnection, limit patient movement and mobility and can also be uncomfortable. The wires connecting the power supply unit to the electrodes limits their separation to the length of the wires provided.
More recently, small self-contained electrotransport delivery devices adapted to be worn on the skin, sometimes unobtrusively under clothing, for extended periods of time have been proposed. The electrical components in such miniaturized electrotransport drug delivery devices are also preferably miniaturized, and may be either integrated circuits (ie, microchips) or small printed circuits. Electronic components, such as batteries, resistors, pulse generators, capacitors, etc, are electrically connected to form an electronic circuit that controls the amplitude, polarity, timing, waveform shape, etc of the electric current supplied by the power source. Such small self-contained electrotransport delivery devices are disclosed for example in Tapper U.S. Pat. No. 5,224,927; Sibalis et al U.S. Pat. No. 5,224,928 and Haynes et al U.S. Pat. No. 5,246,418. Unfortunately, as electrotransport delivery devices become smaller, the power source (eg, batteries) used to power the devices, must also become smaller and hence, battery capacity and battery life become more of a design problem.
In addition to electrotransport devices becoming smaller, there have recently been suggestions to utilize electrotransport devices having a reusable controller which is adapted to be used with multiple drug-containing units. The drug-containing units are simply disconnected from the controller when the drug becomes depleted and a fresh drug-containing unit is thereafter connected to the controller. In this way, the relatively more expensive hardware components of the device (eg, batteries, LED's, circuit hardware, etc) can be contained within the reusable controller, and the relatively less expensive donor reservoir and counter reservoir matrices can be contained in the disposable drug containing unit thereby bringing down the overall cost of electrotransport drug delivery. Examples of electrotransport devices comprised of a reusable controller adapted to be removably connected to a drug-containing unit are disclosed in Sage, Jr. et al, U.S. Pat. No. 5,320,597; Sibalis, U.S. Pat. No. 5,358,483; Sibalis et al, U.S. Pat. No. 5,135,479 (FIG. 12); and Devane et al UK Patent Application 2, 239 803.